This invention relates broadly to the art of knife gate valves and more particularly to gaskets for attaching knife gate valves to pipes and also to devices which allow fine regulation of flow through knife gate valves.
Knife gate valves have long been preferred for controlling the flow of certain materials and also under certain environmental conditions. For example, knife gate valves are often used in slurry-pipe systems. In this respect, knife gate valves have the advantage of quickly providing large openings through pipe strings while not being especially sensitive to jams and malfunctions caused by larger particles in a flow. Also, knife gate valves require very little axial, face plate to face plate, space along a pipe string. It is known, however, that under normal circumstances knife gate valves have the disadvantage that one can usually not finely regulate the flow of material therethrough. In this regard when a knife-gate blade is lifted only slightly its broad tip rises from a seat allowing a great deal of flow therethrough. A number of devices have been suggested for converting a knife gate valve into a throttling (finely controlled) knife gate valve which allows finer control of flow therethrough. In this respect, most of these systems concern the attachment of plates to a knife-gate-valve seat or frame, to create a V-shaped baffle in the flow passage next to the knife-gate blade. As the blade of such a modified valve is lifted, the tip of the V-opening is first uncovered, rather than providing a wide crescent-shaped opening as with most knife gate valves, thereby providing a small flow. As the gate is further lifted, the sloping sides of the V-opening are uncovered to slowly increase flow. One such system is described in U.S. Pat. No. 2,883,148 to Williams, however, there are many other such systems in the prior art. Many of these systems involve the welding of plates in knife-gate flow passages, however, Williams employs a metal insert which is inserted from outside a valve frame into its flow passage to form a V-shaped opening at the knife gate blade and to have a flange which covers a face plate of the knife gate valve. The insert flange is then clamped between a pipe flange and the knife-gate valve face plate to form a sealing connection therewith. Further, the inner end of Williams' insert must make contact with a resilient seat member to prevent the flow of slurry about the insert which would otherwise allow accumulation of solids thereabout. A locating pin extending from the flange of the insert fits into a hole in the knife gate valve face plate to properly orient the insert. Although Williams' insert offers simplicity and flexibility over systems involving welding, it is not generally used because it has a number of significant disadvantages. One disadvantage of Williams' insert is that it can only be used with certain knife gate valves, and most likely would require a specially made knife gate valve. The reason for this is that this insert must make sealing contact with a resilient seat member positioned at the knife-gate blade. If a knife gate valve does not have this resilient seat member, fluid controlled with the knife gate valve will flow about the insert thereby causing the accumulation of solids, jamming the valve after significant use. Further, Williams' insert relies on the use of a finely machined pipe flange, a finely machined insert flange (on both sides), and a finely machined valve face plate to obtain a proper metal-to-metal seal. Such machining of metal is labor intensive and extremely expensive. Yet another problem with Williams' insert is that it has a fixed, unadjustable, dimension from its the V-shaped opening to its flange. Unfortunately, this distance is not the same for all valves and even if it were tolerances would vary between valves of the same make. These different dimensions and tolerances do not always allow the flange and V-shaped opening of Williams' insert to form a good seal with a face plate and simultaneously make sliding engagement with a valve blade. Similarly, it is not possible to adjust Williams' insert at work locations because his V-forming baffle and his insert flange cannot be moved relative to one another.
It is an object of this invention to provide a one-piece throttling insert which serves as a resilient gasket between a knife gate valve face plate and a pipe flange and which also provides its own gasket to form an axial seal with the knife gate valve flow passage and sliding engagement with a knife gate valve blade. Further, it is an object of this invention to provide such an insert which does not have to be unduly machined to provide a metal-to-metal sealing surfaces but which allows adjustment at an inner V-shaped passage forming end seat to accommodate various distances between face plates of knife gate valves and the blades thereof. Further, it is an object of this invention to provide such a throttling insert which is inexpensive to manufacture, easy to use, but which is extremely effective in use for metering fluid flow through a knife gate valve without allowing undue jamming thereof.